Over the course of about 5 days, my boys took off on the project. My husband outlined a plan, based on simple guidance from the Internet. It was great that we had absolutely everything in the house, mostly because of the model railroading supplies we had just used on our son’s model railroad that was completed late last year.

The teacher offered us a recipe for salt dough, which is a popular method for making the volcanoes. Instead we chose paper mache, which is more lightweight.

We started with several items that were essentially recycled: an empty soda bottle, a leftover piece of plywood for the base, a cardboard box and our old phone book.

A few years ago, when the kids were studying chemistry, we made Hamantashen cookies for Purim and the question came up about the difference between baking soda and baking powder. We had done the baking soda and vinegar thing many times, so we already knew that mixing sodium bicarbonate with an acid releases carbon dioxide. When you bake, those little bubbles of CO2 make the bread puff up. The acid needed to start the reaction in a batter can come from yogurt, buttermilk, lemon juice, or even molasses or honey.

Baking powder = baking soda + cream of tartar. Image: Kathy Ceceri

But the recipe for Hamentashen from my grandmother’s old cookbook called for baking powder:

Mix together everything except the flour. Add enough flour to make a soft dough, a little on the dry side.

Form into a ball. Roll out about 1/4 inch thick on a floured board. Cut the dough into circles with a round cookie cutter or the rim of a glass. My grandmother’s were always small and dainty, but in New York the bakeries they make ‘em as big as your hand.

Spoon some filling in the middle. To shape the cookie, pinch three sides up to form a triangle.

Bake for 20 minutes, until the edges are brown.

Baking powder fizzes with water alone. Image: Kathy Ceceri

Baking powder is baking soda with the acid already mixed in, in the form of cream of tartar. When moistened, powdered acid combines with the baking soda and produces the requisite bubbles. Some baking powder is “double acting,” meaning it releases most of the bubbles when heated, so that the leavening action doesn’t expend itself while the dough is waiting on the counter to bake.

Purim starts tonight at sundown. If you want to try my grandmother’s recipe for Hamantashen and you’re all out of baking powder, you can make your own by mixing two parts cream of tartar with one part baking soda.